U.S. patent application number 10/922082 was filed with the patent office on 2005-09-01 for phosphor, light source and led.
This patent application is currently assigned to DOWA MINING CO., LTD.. Invention is credited to Gotoh, Masahiro, Nagatomi, Akira, Sakane, Kenji, Yamashita, Shuji.
Application Number | 20050189863 10/922082 |
Document ID | / |
Family ID | 34879788 |
Filed Date | 2005-09-01 |
United States Patent
Application |
20050189863 |
Kind Code |
A1 |
Nagatomi, Akira ; et
al. |
September 1, 2005 |
Phosphor, light source and LED
Abstract
A phosphor with high efficiency having an excitation band
corresponding to light of the ultraviolet-visible (300 to 550 nm)
wavelength region emitted from a light emitting portion which emits
blue or ultraviolet light is provided. A nitride of Ca, a nitride
of Al, a nitride QfSi, and an oxide of Eu are prepared, and
respective raw materials are weighed so that a mol ratio of
respective elements becomes Ca:Al:Si:Eu=0.985:3:1:0.0- 15, mixed
under a nitrogen atmosphere, and thereafter fired at 1500.degree.
C. in a nitrogen atmosphere to thereby produce a phosphor having a
composition formula Ca.sub.0.985SiAlN.sub.3:Eu0.015.
Inventors: |
Nagatomi, Akira; (Tokyo,
JP) ; Sakane, Kenji; (Tokyo, JP) ; Gotoh,
Masahiro; (Tokyo, JP) ; Yamashita, Shuji;
(Tokyo, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
DOWA MINING CO., LTD.
Tokyo
JP
|
Family ID: |
34879788 |
Appl. No.: |
10/922082 |
Filed: |
August 20, 2004 |
Current U.S.
Class: |
313/486 |
Current CPC
Class: |
C09K 11/7734 20130101;
C09K 11/0883 20130101 |
Class at
Publication: |
313/486 |
International
Class: |
H01L 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
JP |
2004-55536 |
Claims
1. A phosphor represented by a general formula M-A-B--N:Z, wherein
the element M is a divalent element, the element A is a trivalent
element, the element B is a tetravalent element, the N is nitrogen,
and the element Z is an activator in the phosphor.
2. The phosphor according to claim 1, wherein when the phosphor is
represented by a composition formula MmAaBbNn: Zz, the phosphor has
a composition ratio (m+z):a:b:n=1:1:1:3.
3. The phosphor according to claim 1, wherein the element M is at
least one or more elements selected from the group consisting of
beryllium, magnesium, calcium, strontium, barium, zinc, cadmium,
and mercury, wherein the element A is at least one or more elements
selected from the group consisting of boron, aluminum, gallium,
indium, thallium, yttrium, scandium, phosphorus, arsenic, antimony,
and bismuth, wherein the element B is at least one or more elements
selected from the group consisting of carbon, silicon, germanium,
tin, titanium, hafnium, molybdenum, tungsten, chromium, lead, and
zirconium, and wherein the element Z is at least one or more
elements selected from rare-earth elements or transition metal
elements.
4. The phosphor according to claim 1, wherein the element A is
aluminum and the element B is silicon.
5. The phosphor according to claim 1 wherein a host material
structure of the phosphor does not include oxygen.
6. The phosphor according to claim 2, wherein a value of a mol
ratio: z/(m+z) of the element M and the activator element Z is in a
range from 0.0001 to 0.5.
7. The phosphor according to claim 1, wherein the element M is at
least one or more elements selected from the group consisting of
magnesium, calcium, strontium, barium, and zinc.
8. The phosphor according to claim 1, wherein the element Z is at
least one or more elements selected from the group consisting of
europium, manganese, and cerium.
9. The phosphor according to claim 8, wherein the element Z is
europium.
10. The phosphor according to claim 9, wherein the element M is
calcium, the element A is aluminum, and the element B is
silicon.
11. The phosphor according to claim 1, wherein the phosphor is in a
powder form.
12. The phosphor according to claim 11, wherein an average particle
size of the phosphor is 20 .mu.m or smaller and 1 .mu.m or
larger.
13. A light source, comprising: a phosphor according to claim 1;
and a light emitting portion emitting light of a first wavelength,
wherein a part of the light of the first wavelength is used as an
excitation source to make said phosphor emit light having a
wavelength which is different from the first wavelength.
14. The light source according to claim 13, wherein the first
wavelength is a wavelength of from 300 nm to 550 nm.
15. A light emitting diode, comprising: a phosphor according to
claim 1; and a light emitting portion emitting light of a first
wavelength, wherein a part of the light of the first wavelength is
used as an excitation source to make said phosphor emit light
having a wavelength which is different from the first
wavelength.
16. The light emitting diode according to claim 15, wherein the
first wavelength is a wavelength of from 300 nm to 550 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a phosphor used in a
display device such as an LED, CRT, PDP, FED, and EL, and a
lighting unit such as a vacuum fluorescent display (VFD) and
fluorescent lamp, the phosphor being particularly suitable for an
LED, a light source, and a lighting unit each of which has a light
emitting portion of ultraviolet-blue light or the like and emits
visible or white light.
[0003] 2. Description of the Related Art
[0004] An LED, a light source and a lighting unit are known, which
emit white light by a combination of a light emitting element which
emits blue or ultraviolet light and a phosphor which has an
excitation band in the ultraviolet-blue wavelength region generated
from the light emitting element.
[0005] As the phosphor used in the LED and the like,
Y.sub.2O.sub.2S:Eu, La.sub.2O.sub.2S:Eu,
3.5MgO.0.5MgF.sub.2.GeO.sub.2:Mn, and (La, Mn, Sm).sub.2O.sub.2S
.Ga.sub.2O.sub.3 are known as a red phosphor, ZnS:Cu,Al,
SrAl.sub.2O.sub.4:Eu, and BAM:Eu,Mn are known as a green phosphor,
YAG:Ce is known as a yellow phosphor, and BAM:Eu, Si.sub.5
(PO.sub.4).sub.3Cl:Eu, ZnS:Ag, and (Sr, Ga, Ba,
Mg).sub.10(PO.sub.4).sub.- 6Cl:Eu are known as a blue phosphor.
Then, an LED, a light source and a lighting unit of white or
monochromatic light can be obtained by combining these phosphors
and a light emitting element.
[0006] As a phosphor for a white LED, there are suggested an
oxynitride glass phosphor (refer to Patent Document 1) a phosphor
having asialon as a host material (refer to Patent Documents 2 and
3), and a phosphor including, nitrogen of a silicon nitride group
or the like (refer to Patent Documents 4 and 5), and there is
further suggested a lighting device using these phosphors.
[0007] [Patent Document 1] Japanese Patent Application Laid-open
No. 2001-214162
[0008] [Patent Document 2] Japanese Patent Application Laid-open
No. 2003-336059
[0009] [Patent Document 3] Japanese Patent Application Laid-open
No. 2003-124527
[0010] [Patent Document 4] Translated National Publication of
Patent Application No. 2003-515655
[0011] [Patent Document 5] Japanese Patent Application Laid-open
No. 2003-277746
SUMMARY OF THE INVENTION
[0012] With respect to the above-described LED and light source
which emit visible light or white light by a combination of a light
emitting portion which emits blue or ultraviolet light and a
phosphor which has an excitation band corresponding to light of the
ultraviolet-blue wavelength region generated from the light
emitting portion, it is strongly demanded to improve not only the
emission efficiency of the light emitting portion but also the
emission efficiency of the phosphor, in order to improve luminance
of the visible light or white light.
[0013] Hereinafter, the phosphor will be described with an example
of an LED which emits white light by a combination of a light
emitting element which emits blue or ultraviolet light and a
phosphor.
[0014] In the case that the phosphor is used as a phosphor for a
white LED, luminance of the entire white LED is improved by the
emission efficiency of the phosphor, so that a phosphor which emits
light with better efficiency with respect to the emission
wavelength of the light emitting element has been demanded.
[0015] For example, an excitation band of YAG:Ce based yellow
phosphor is in an efficient excitation range when emitting light by
blue light of a light emitting element of an LED, and thus it can
produce good yellow light emission. However, when emitting light by
ultraviolet light of a light emitting element of an LED, it
deviates from the excitation range, so that it cannot produce high
light emission.
[0016] Further, regarding a red phosphor, existing phosphors have
poor emission efficiency, so that when it is mixed with a phosphor
of different color, there is adopted a method to compensate a light
emitting amount by increasing the compounding ratio of the phosphor
of a red component. However, a phosphor with higher efficiency has
been demanded.
[0017] The present invention is made in view of the above-described
situation, and an object thereof is to provide a phosphor with high
efficiency having an excitation band corresponding to light of the
ultraviolet-visible (300-550 nm) wavelength region emitted from a
light emitting element which emits blue or ultraviolet light.
[0018] As a result of study on host material compositions of
various phosphors with respect to the above-described object, the
inventors of the present invention devised a phosphor with higher
efficiency and an excellent light emitting characteristic, which
has a new host material composition.
[0019] According to a first aspect of the present invention, a
phosphor represented by a general formula M-A-B--N:Z is provided,
wherein the element M is a divalent element; the element A is a
trivalent element, the element B is a tetravalent element, the N is
nitrogen, and the element Z is an activator in the phosphor.
[0020] According to a second aspect of the present invention, the
phosphor described in the first aspect is provided, wherein when
the phosphor is represented by a composition formula MmAaBbNn:Zz,
the phosphor has a composition ratio (m+z):a:b:n=1:1:1:3.
[0021] According to a third aspect of the present invention, the
phosphor described in the first or the second aspect is
provided,
[0022] wherein the element M is at least one or more elements
selected from the group consisting of beryllium, magnesium,
calcium, strontium, barium, zinc, cadmium, and mercury,
[0023] wherein the element A is at least one or more elements
selected from the group consisting of boron, aluminum, gallium,
indium, thallium, yttrium, scandium, phosphorus, arsenic, antimony,
and bismuth,
[0024] wherein the element B is at least one or more elements
selected from the group consisting of carbon, silicon, germanium,
tin, titanium, hafnium, molybdenum, tungsten, chromium, lead, and
zirconium, and
[0025] wherein the element Z is at least one or more elements
selected from rare-earth elements or transition metal elements.
[0026] According to a fourth aspect of the present invention, the
phosphor described in any one of the first to the third aspect is
provided, wherein the element A is aluminum and the element B is
silicon.
[0027] According to a fifth aspect of the present invention, the
phosphor described in any one of the first to the fourth aspect is
provided, wherein a host material structure of the phosphor does
not include oxygen.
[0028] According to a sixth aspect of the present invention, the
phosphor described in any one of the second to the fifth aspect is
provided, wherein a value of a mol ratio: z/(m+z) of the element M
and the activator element Z is in a range from 0.0001 to 0.5.
[0029] According to a seventh aspect of the present invention, the
phosphor described in any one of the first to the sixth aspect is
provided, wherein the element M is at least one or more elements
selected from the group consisting of magnesium, calcium,
strontium:, barium, and zinc.
[0030] According to an eighth aspect of the present invention, the
phosphor described in any one of the first to the seventh aspect is
provided, wherein the element Z is at least one or more elements
selected from the group consisting of europium, manganese, and
cerium.
[0031] According to a ninth aspect of the present invention, the
phosphor described in the eighth aspect is provided, wherein the
element Z is europium.
[0032] According to a tenth aspect of the present invention, the
phosphor described in the ninth aspect is provided, wherein the
element M is calcium, the element A is aluminum, and the element B
is silicon.
[0033] According to an eleventh aspect of the present invention,
the phosphor described in any one of the first to the tenth aspect
is provided, wherein the phosphor is in a powder form.
[0034] According to a twelfth aspect of the present invention, the
phosphor described in the eleventh aspect is provided, wherein an
average particle size of the phosphor is 20 .mu.m or smaller and 1
.mu.m or larger.
[0035] According to a thirteenth aspect of the present invention, a
light source is provided, which comprises:
[0036] a phosphor described in any one of the first to the twelfth
aspect; and
[0037] a light emitting portion emitting light of a first
wavelength,
[0038] wherein a part of the light of the first wavelength is used
as an excitation source to make the phosphor emit light having a
wavelength which is different from the first wavelength.
[0039] According to a fourteenth aspect of the present invention,
the light source described in the thirteenth aspect is provided,
wherein the first wavelength is a wavelength of from 300 nm to 550
nm.
[0040] According to a fifteenth aspect of the present invention, a
light emitting diode is provided, which comprises:
[0041] a phosphor described in any one of the first to the twelfth
aspect; and
[0042] a light emitting portion emitting light of a first
wavelength,
[0043] wherein a part of the light of the first wavelength is used
as an excitation source to make the phosphor emit light having a
wavelength which is different from the first wavelength.
[0044] According to a sixteenth aspect of the present invention,
the light emitting diode described in the fifteenth aspect is
provided, wherein the first wavelength is a wavelength of from 300
nm to 550 nm.
[0045] The phosphor represented: by a general formula M-A-B--N:Z
according to the first to the eleventh aspect has an excitation
band corresponding to ultraviolet-blue light (wavelength region of
from 300 to 550 nm) emitted by a light emitting element which emits
blue or ultraviolet light, and emits light with high efficiency.
Therefore, by combining the phosphor with a light emitting portion
which emits the ultraviolet-blue light, an LED, a light source and
a lighting unit of monochromatic light or white light with high
efficiency and high luminance can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a graph of an emission spectrum of a phosphor
according to the present invention;
[0047] FIG. 2 is a graph of an excitation spectrum of the phosphor
according to the present invention;
[0048] FIG. 3 is a graph of a composition and luminescence
intensity of the phosphor according to the present invention;
and
[0049] FIG. 4 is a graph of emission spectra of phosphors according
to the present invention and a conventional art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] A phosphor according to the present invention is a phosphor
having a quaternary host material structure represented by a
general formula M-A-B--N:Z.
[0051] Here, the element M is a divalent element in the phosphor.
The element A is a trivalent element in the phosphor. The element B
is a tetravalent element in the phosphor. N is nitrogen. The
element Z operates as an activator in the phosphor. When the
phosphor has this host, material structure, it becomes a phosphor
having high emission efficiency.
[0052] Furthermore, when the above-described host material
structure of the phosphor has a chemically stable structure, it is
unlikely to have an uneven phase, so that emission efficiency does
not decrease. Therefore, it is a preferable structure. Then, when
the phosphor is represented by a composition formula MmAaBbNn:Zz,
the phosphor is preferred to have a composition ratio
(m+z):a:b:n=1:1:1:3, in order to make the host material structure
of the phosphor have a chemically stable structure. This is because
the element M is a divalent element, the element A is a trivalent
element, and the element B is a tetravalent element, which combine
with trivalent nitrogen to be a stable nitrogen compound. However,
it is conceivable that a slight displacement in composition may
occur.
[0053] Here, since a divalent metal nitride normally takes a
chemical formula M.sub.3N.sub.2, a trivalent metal nitride takes a
chemical formula AN, and the tetravalent metal nitride takes a
chemical formula B.sub.3N.sub.4, the respective nitrides may be
mixed by a mol ratio of 1:3:1 so that they become M:A:B=1:1:1.
However, the element Z replaces a part of the element M when a
divalent element is used as an activator for example, so that it
becomes (m+z):a:b:n=1:1:1:3.
[0054] Thus, it is conceivable that the chemically stable structure
can be achieved, and the phosphor with high efficiency and high
luminance can be obtained.
[0055] The element M is preferably at least one or more elements
selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd,
and Hg. In other words, the element M may be single Ca, or may be a
mixture of Ca, Mg . . . , and the like for example.
[0056] The element A is preferably at least one or more elements
selected from the group consisting of B (boron), Al, Ga, In, Ti, Y,
Sc, P, As, Sb, and Bi. In other words, the element A may be single
Al, or may be a mixture of Al, Ga . . . , and the like for
example.
[0057] The element B is preferably at least one or more elements
selected from the group consisting of C, Si, Ge, Sn, Ni, Hf, Mo, W,
Cr, Pb, and Za. In other words, the element B may be single Si, or
may be a mixture of Si, Ge . . . , and the like for example.
[0058] The element Z is preferably at least one or more elements
selected from rare-earth elements and transition metal elements. In
other words, the element Z may be single Eu, or may be a mixture of
Eu, La . . . , and the like for example.
[0059] By the element M, element A, element B, and element Z having
the above-described structure, the emission efficiency of the
phosphor increases further.
[0060] Respective nitrides of Al as the element A and Si as the
element B are generally used in thermally conductive materials and
structural materials, and they are easily obtainable and cheap. In
addition, their environmental loads are low. Therefore, by
selecting these elements as a raw material, cheap and easily usable
phosphor can be obtained, so that it is a preferable
composition.
[0061] As is clear from the general formula M-A-B--N:Z, the
phosphor according to the present invention does not include oxygen
in the constituting elements, and it is a different composition
group from a conventional phosphor having a sialon group host
material (Si--Al--O--N group) and phosphor having a Si--O--N group
host material. According to the study conducted by the inventors of
the present invention, it is found that when the oxygen content in
the phosphor is large, the emission efficiency decreases and the
emission wavelength of the phosphor tends to shift to a shorter
wavelength side. From this point of view, the phosphor according to
the present invention which includes no oxygen in the host material
constituting elements has higher emission efficiency and can avoid
the shift of the emission wavelength to the shorter wavelength
side, so that it is a preferable composition.
[0062] In the phosphor according to the present invention, a mol
ratio z/(m+z) of the element M and the activator element Z are
preferred to be in a range from 0.0001 to 0.5. When the mol ratio
z/(m+z) of the element M and the activator element Z is in that
range, it is possible to avoid decrease of emission efficiency due
to concentration quenching caused by an excessive content of the
activator, and on the other hand, it is also possible to avoid
decrease of emission efficiency due to an excessively small amount
of light emission contributing atoms caused by an excessively small
content of the activator. Depending on the type of the activating
element Z to be added, an optimum percentage of z/(m+z) differs
slightly, and more preferably, good light emission can be produced
when it is in a range from 0.0005 to 0.1.
[0063] When the element M of the phosphor of the present invention
is at least one or more elements selected from the group consisting
of Mg, Ca, Sr, Ba, and Zn, a raw material can be easily obtained
and an environmental load is low, so that it is a preferable
composition.
[0064] When the element Z of the phosphor of the present invention
is at least one or more elements selected from the group consisting
of Eu, Mn, and Ce, emission efficiency of the phosphor becomes
high, so that it is a preferable composition.
[0065] When the element Z of the phosphor of the present invention
is Eu, the emission wavelength exhibits red wavelength, so that a
red based phosphor for a white light emitting unit with good
emission efficiency can be obtained, and thus it is a preferable
composition.
[0066] When the element M is Ca, the element A is Al, the element B
is Si, and the element Z is Eu in the phosphor of the present
invention, raw materials can be easily obtained and an
environmental load is low, and the emission wavelength of the
phosphor exhibits red wavelength, so that a red based phosphor
capable of producing white light with good emission efficiency can
be obtained, and thus it is a preferable composition.
[0067] When the phosphor according to the present invention is in a
powder form, the average particle size of the powder is preferred
to be 20 .mu.m or smaller. This is because light emission of the
phosphor powder is is considered to occur mainly on the surface of
a particle, and a surface area of the phosphor powder per unit
weight becomes smaller when the average particle size is larger
than 20 .mu.m. Further, according to the study conducted by the
inventors of the present invention, emission efficiency decreases
also when the average particle size is 1 .mu.m or smaller.
Accordingly, the average particle size of the phosphor powder of
the present invention being 20 .mu.m or smaller and 1 .mu.m or
larger is a preferable composition.
[0068] In addition, when considering a case that the phosphor
powder is used as phosphor powder for an LED, the phosphor powder
is mixed with resin to be applied on the LED, and then, also from a
point of view to obtain good applicability, the average particle
size is preferred to be 20 .mu.m or smaller and 1 .mu.m or
larger.
[0069] By combining the phosphor obtained according to the present
invention with, for example, a light source which emits blue or
ultraviolet light, a light source of monochromatic visible light or
white light with high efficiency can be produced.
[0070] The phosphor obtained according to the present invention
emits light upon reception of light in a wide excitation range from
300 to 550 nm, so that a light source of monochromatic visible
light or white light with high efficiency can be produced by
combining the phosphor with, for example, a light source which
emits blue or ultraviolet light.
[0071] By combining the phosphor obtained according to the present
invention with, for example, an LED light emitting portion which
emits blue or ultraviolet light, an LED of monochromatic visible
light or white light with high efficiency can be produced.
[0072] The phosphor obtained according to the present invention
emits light upon reception of light in a wide excitation range from
300 to 550 nm, so that an LED of monochromatic visible light or
white light with high efficiency can be produced by combining the
phosphor with an LED light emitting portion which emits blue or
ultraviolet light.
[0073] (Production Method of the Phosphor)
[0074] A production method of the phosphor according to the present
invention will be described with an example of producing
CaAlSiN.sub.3:Eu (when z/(m+z)=0.015).
[0075] First, nitrides of the element M, element A, and element B
are prepared. The respective nitrides may be a commercially
available raw material. Since they are preferred to have high
purity, raw materials of 2N or higher, or more preferably 3N or
higher are prepared. As a raw material of the element Z, an oxide
may be prepared, which may be a commercially available raw
material. Since it is preferred to have high purity, a raw material
of 2N or higher, or more preferably 3N or higher is prepared.
[0076] When CaAlSiN.sub.3:Eu is produced, Ca.sub.3N.sub.2 (2N), AlN
(3N), and Si.sub.3N.sub.4 (3N) may be prepared as nitrides of the
element. M, element A, and element B respectively. As the element
Z, Eu.sub.2O.sub.3 (3N) may be prepared.
[0077] These raw materials are weighed and mixed so that a mol
ratio of the respective elements becomes M:A:B:Z=0.985:3:1:0.015.
As a matter of course, the value 0.985 of the element M and the
value 0.015 of the element Z are set corresponding to the set value
of z/(m+z)=0.015, and they vary according to variation of the set
value.
[0078] The mixing may be performed by a general mixing method using
a mortar or the like, and is performed under an inert atmosphere of
nitrogen or the like. Operation inside a glove box under an inert
atmosphere is convenient.
[0079] The raw materials after being completely mixed are heated to
1500.degree. C. by a heating rate of 15.degree. C./min under an
inert atmosphere of nitrogen or the like, and retained and fired at
1500.degree. C. for three hours. After the burning is completed,
the raw materials are cooled down from 1500.degree. C. to
200.degree. C. for an hour, further cooled down to the room
temperature, and thereafter pulverized using a pulverizing means
such as a mortar, ball mill, or the like to have a predetermined
average particle size (preferably, from 20 .mu.m to 1 .mu.m) to
thereby produce a phosphor of a composition formula
Ca.sub.0.955SiAlN.sub.3:EU.sub.0.010.
[0080] When the element M, the element A, the element B, and the
element Z are replaced with other elements, a predetermined
phosphor can be produced by a similar production method by setting
compounding amounts of the respective raw materials to a
predetermined composition formula at the time of preparation, even
when set values of z/(m+z) vary.
EXAMPLES
[0081] Hereinafter, the present invention will be described more
specifically based on examples.
Example 1
[0082] Commercially available Ca.sub.3N.sub.2 (2N), AlN (3N),
Si.sub.3N.sub.4 (3N), and EU.sub.2O.sub.3 (3N) were prepared, and
respective raw materials were weighed so that the mol ratio of
respective elements becomes Ca:Al:Si:Eu=0.985:3:1:0.015 and mixed
using a mortar inside a glove box under a nitrogen atmosphere. The
mixed raw materials were heated to 1500.degree. C. by a heating
rate of 15.degree. C./min in a nitrogen atmosphere, retained and
fired at 1500.degree. C. for three hours, and cooled down
thereafter from 1500.degree. C. to 200.degree. C. for an hour to
obtain a phosphor of the composition formula
Ca.sub.0.985SiAlN.sub.3:Eu.sub.0.015. Results of analysis of the
obtained phosphor powder are shown in Table 1.
[0083] The average particle size (D50) of the obtained phosphor was
4.65 .mu.m, and the specific surface area thereof was 1.13
m.sup.2/g, and 2.2% of the total weight was occupied by oxygen as
an impurity.
1 TABLE 1 Average particle Specific Ca Al Si N Eu O size surface
(%) (%) (%) (%) (%) (%) Others (D50) area Ca.sub.0.985AlSiN.sub.3:
Eu.sub.0.015 27.3 20.5 19.2 29.2 1.46 2.2 0.1 4.65 .mu.m 1.13
m.sup.2/g
[0084] Next, an emission spectrum and an excitation spectrum of the
phosphor of the present invention were measured. Results of the
measurement will be described with reference to FIG. 1 and FIG. 2.
Here, in both FIG. 1 and FIG. 2, luminescence intensity of the
phosphor of the present invention is taken on the vertical axis,
and a wavelength of light is taken on the horizontal axis.
[0085] First, the emission spectrum of the phosphor according to
the present invention will be described using FIG. 1. The emission
spectrum is a spectrum emitted from an object when the object is
irradiated with light or energy having a certain wavelength. FIG. 1
shows a wavelength spectrum emitted from the phosphor of the
present invention when the phosphor is irradiated with
monochromatic light of 450 nm.
[0086] As is clear from FIG. 1, the phosphor exhibits light
emission in a wide wavelength region from 550 nm to 800 nm, and
exhibits the highest light emission at 656 nm. Incidentally, red
light emission color was recognized by visual observation.
[0087] Next, the excitation spectrum of the phosphor of the present
invention will be described using FIG. 2. The excitation spectrum
is a spectrum measured in such a manner that a phosphor that is a
subject to be measured is excited using monochromatic light of
various wavelengths, luminescence intensity with a constant
wavelength of light emission from the phosphor is measured, and
excitation wavelength dependency of the luminescence intensity is
measured. In this measurement, the phosphor of the present
invention was irradiated with monochromatic light of from 250 nm to
570 nm, and excitation dependency of the luminescence intensity of
light with a wavelength of 656 nm emitted from the phosphor was
measured.
[0088] As is clear from FIG. 2, the excitation spectrum of the
phosphor is wide, from approximately 300 nm to 600 nm, and it was
found that the phosphor exhibits high emission of red light in a
wide range of the excitation band from approximately 300 nm to 600
nm.
Example 2
[0089] In Example 2, the phosphor according to the present
invention having a composition formula Ca.sub.mSiAlN.sub.3:Eu was
used to measure the luminescence intensity depending on
concentration of the activator element Z.
[0090] When producing a measurement sample, addition amounts of Ca
and Eu were adjusted so that the concentration of the activator Eu
has a relationship of m+z=1 with Ca.
[0091] Results of the measurement will be described with reference
to FIG. 3. Here, in FIG. 3, luminescence intensity of the phosphor
of the present invention is taken on the vertical axis, and a value
of Eu/(Eu+Ca), which is a compounding ratio of Ca and Eu, is taken
on the horizontal axis. Note that luminescence intensity when
Eu/(Eu+Ca)=0.015 is set as 100%. Then, results of adjusting the
value of Eu/(Eu+Ca) from 0.0015 to 0.06 are shown. Note that light
having a wavelength of 450 nm was, used for excitation.
[0092] As is clear from the results in FIG. 3, the luminescence
intensity first rises with increase of the value of Eu/(Eu+Ca), but
the luminescence intensity starts to decrease at a peak of
approximately 0.015. A conceivable reason of this is that, at a
portion where the value is less than 0.015, the activator element
is not sufficient, and at a portion where the value is more than
0.015, there occurs concentration quenching caused by the activator
element.
[0093] In addition, in parallel to the measurement of the
luminescence intensity, chromaticity coordinates (x, y) of the
light emission were also measured. Results of the measurement are
shown in Table 2. As is clear from the results in Table 2, it was
confirmed that, as the value of Eu/(Eu+Ca) increases, an emission
maximum also shifts to a longer wavelength side.
2TABLE 2 Ex: 450 nm Eu concen- Relative Emission tration intensity
maximum x y Ca.sub.0.9975AlSiN.sub.3: Eu.sub.0.0015 0.0015 28.8%
632.7 0.608 0.384 Ca.sub.0.9925AlSiN.sub.3: Eu.sub.0.0075 0.0075
75.5% 644.3 0.651 0.346 Ca.sub.0.985AlSiN.sub.3: Eu.sub.0.015
0.0150 100.0% 651.3 0.671 0.327 Ca.sub.0.97AlSiN.sub.3: Eu.sub.0.03
0.0300 77.0% 660.0 0.683 0.315 Ca.sub.0.94AlSiN.sub.3: Eu.sub.0.06
0.0600 54.1% 670.2 0.691 0.306
Example 3
[0094] On an LED of ultraviolet light having a nitride
semiconductor as a light emitting portion, the phosphor obtained
according to the present invention, a commercially available blue
phosphor (BAM:Eu), and a commercially available green phosphor
(ZnS:Cu, Al) were applied, and the LED of ultraviolet light was
illuminated. Then, the respective phosphors emitted light by light
from the LED, and an LED which appears to be white when visually
observed due to a spectrum of emission wavelength was obtained.
[0095] Further, on an LED of blue light having a nitride
semiconductor as a light emitting portion, the phosphor obtained in
the present invention and a commercially available yellow phosphor
(YAG:Ce) were applied, and the LED of blue light was illuminated.
Then, the respective phosphors emitted light by light from the LED,
and a reddish LED having a low color temperature when visually
observed was obtained.
Example 4
[0096] In Example 4, the phosphor according to the present
invention and a Ca.sub.2Si.sub.5N.sub.8:Eu phosphor disclosed in
Patent Documents 4 and 5 were compared.
[0097] It should be noted that, for the Ca.sub.2Si.sub.5N.sub.8:Eu
phosphor used in this example, 2N or 3N reagents, of
Ca.sub.3N.sub.7, Si.sub.3N.sub.4, and EU.sub.2O.sub.3 were prepared
as raw materials, and the respective raw materials were weighed so
that Ca, Si, and Eu have a mol ratio of 1.97:5:0.03 and mixed by a
mortar inside a glove box under a nitrogen atmosphere. The mixed
raw materials were fired at 1500.degree. C. in nitrogen for three
hours and then cooled down and pulverized similarly to Example 1 to
thereby produce a phosphor of a composition-formula
Ca.sub.1.97Si.sub.5N.sub.8:Eu.sub.0.03.
[0098] Results of an analysis of the phosphor of the composition
formula Ca.sub.0.985SiAlN.sub.3:Eu0.015 according to the present
invention which is produced in Example 1 and the phosphor of the
composition formula Ca.sub.1.97Si.sub.5N.sub.8:Eu.sub.0.03 are
shown in parallel in Table 3.
[0099] As is clear from the results in Table 3, contents of oxygen
and other elements as impurities in both the produced phosphors
were approximately the same, and specific surface areas of both the
phosphors were also approximately the same.
3 TABLE 3 Average particle Specific Ca Al Si N Eu O size surface
(%) (%) (%) (%) (%) (%) Others (D50) area Ca.sub.0.985AlSiN.sub.3:
Eu.sub.0.015 27.3 20.5 19.2 29.2 1.46 2.2 0.1 4.65 .mu.m 1.13
m.sup.2/g Ca.sub.1.97Si.sub.5N.sub.8: Eu.sub.0.03 22.3 0.3 39.6
34.2 1.34 2.1 0.2 4.77 .mu.m 1.11 m.sup.2/g
[0100] Next, emission spectra of both the above-described phosphors
were measured and compared similarly to Example 1. However,
monochromatic light of 460 nm was used as light to be irradiated.
Results of the measurement are shown in FIG. 4 and Table 4.
[0101] FIG. 4 is a graph similar to FIG. 1, in which the emission
spectrum of the phosphor according to the present invention is
shown by a solid line, and the emission spectrum of the phosphor of
the composition formula Ca.sub.1.97Si.sub.5N.sub.8:Eu.sub.0.03 is
shown by a dashed line.
4 TABLE 4 Excitation wave Relative Emission Chromaticity length
intensity maximum x y Ca.sub.0.985AlSiN.sub.3: Eu.sub.0.015 460 nm
137.4% 656.2 0.671 0.327 Ca.sub.1.97Si.sub.5N.sub.8: Eu.sub.0.03
460 nm 100.0% 609.2 0.593 0.405
[0102] As is clear from the results in FIG. 4 and Table 4, the
phosphor according to the present invention was approximately 40%
higher in relative intensity as compared to the :phosphor of the
composition formula Ca.sub.1.91Si.sub.5N.sub.8:Eu.sub.0.03, and it
was found to be a highly efficient phosphor. More advantageously,
while the phosphor of the composition formula
Ca.sub.1.97Si.sub.5N.sub.8:Eu.sub.0.03 has an emission maximum at
approximately 610 nm and is orange when visually observed, the
phosphor according to the present invention has an emission maximum
at approximately 656 nm, so that it is closer to red. Therefore,
when making a white LED by combining it with another phosphor, a
mixing ratio of a red based phosphor can be reduced.
* * * * *